Do you leave the down tubes on your Bisson pitts stock or do you expand them to match the tubes? I would assume Bisson builds them this way for a reason. Opening them up would decrease back pressure but may help peak rpms. What are your thoughts?
Anyone email Bisson with this very question?

Both the Bisson and Slimline Pitts style mufflers have way too much exhaust exit area. It would benefit fuel tank pressure and noise output levels to restrict them to the same size as a stock muffler.

I use Bisson's and Slim Lines on several Super Tigers (2000's & a 3250) and always block off one stack. Seems to be the only way to get decent transition because otherwise there is to little pressure in the tank. I wish they came with a plug already installed or some neat way to close off the side closest to the engine exhaust. Cheers, Tom.

How about with GAS engines?